Chronicle staffer Jane Tunks, a novice gardener, is using The Chronicle's rooftop garden as her classroom, with Fred Bové and Kevin Bayuk from the San Francisco Permaculture Guild as her teachers. Here is another of her lessons. Read other stories in the series at sfgate.com/columns/chroniclegarden/archive.

Now that summer is almost over, plants in the rooftop garden are flowering and even bolting - a reminder that it's time to save seeds.

The art of seed saving has been practiced for centuries and is a green - and economical - way to harvest and dry seeds from this year's crops for next year's garden.

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But for some gardeners, including me, just the thought of saving seeds can be daunting enough to send us straight to the seed catalog.

Saving seeds doesn't have to be an intimidating task and can even be downright easy - especially when you follow Fred Bové's suggestions for selecting which seeds to save.

Earlier this year, Bové cautioned me not to think about saving seeds too late in the season. Instead of waiting for the last ragtag plants to flower, he instructed me to look out for the biggest, most colorful specimens that were among the first few plants to become ripe.

He urged me to resist harvesting the first beautiful flower, vegetable or herb of any one planting, and allow it to fully mature.

"You want to save the best characteristics (of any plant) and make those the characteristics that you pass on," explained Bové. Depending on the plant, you may want to select for size, flavor or how quickly it takes for the crop to reach maturity. "That way, you're promoting the desired characteristics in the next generation of seeds."

The next important task is identifying a seed that's ready for saving. There are different ways to save seeds, depending on the variety. Plants in the apiaceae family, which includes parsley, fennel and cilantro, will bloom and form umbrella-shaped flowers (called umbels). We had been watching our flat-leaf parsley flower all summer long, as we waited for the seeds to ripen from inside the umbel.

"If you pick them too early, the seeds won't be ripe enough to reproduce - you'll plant them and nothing will happen." To identify seeds that are ready to save, look for flowers that are beginning to drop off. Look more closely and you will see what Bové describes as "little green nubs." These nubs, or seeds, contain all the information for future plants.

Once the plant is cut, there's no more signal coming through the stem saying keep on living. Now it's time to preserve the next generation. Follow the instructions in "How to harvest seeds."

How to harvest seeds

Here are instructions for saving seeds from the apiaceae family, which includes parsley, fennel and cilantro. Bové cautions that you shouldn't attempt to save F1 hybrids or any type of genetically modified seeds, because they won't exhibit traits of the parent plant.

1. Identify the earliest, best-looking and most floriferous plants in your garden.

2. Watch and wait for the plant's seeds to ripen. When the flowers begin to drop away, you will see "little green nubs" - or ripe seeds - within it.

3. Cut the flowering plant with garden shears.

4. Carefully place the flowers upside-down in a small paper bag, ensuring any seeds that fall go directly into the bag.

5. Close the bag and tie a string around the top, leaving a loop at the end.

6. Hang the bag through the loop in a cool, dry place, away from any drafts. Bové hangs his seeds on closet hooks.

7. Examine the seeds every few days. As they dry out, the seeds will fall out of the stems to the bottom of the bag.

8. When the seeds are dry - "about two weeks ought to do it," says Bové - rub the bag, as if you're warming up your hands over a fire. This will further separate the chaff from the seeds.

9. Pour the seeds out of the bag and onto a flat surface - a baking sheet with edges is ideal because seeds won't fall onto the floor.

10. Separate out anything that is not a seed - which can include leaves, stems, chaff and other plant debris.

11. Store in a closed container and label with the year and type of seed. If stored away from moisture, most seeds will be viable from three to five years.

12. Put your seed in the ground during the next planting season. Enjoy.

More varieties to save

Bové shared with us quick tips on how to save other seed types.

Beans and peas: The easiest seeds to save - just wait for the seedpod to swell up and dry out.

Brassicas: The brassica family includes cabbage, mustard, kale and broccoli. They have "seedheads" that can be saved and stored like apiaceae family plants.

Melon and pumpkins: Remove the seeds, clean and dry.

Note: Some seeds, like lettuces and radicchio, are small and fiddly and therefore harder to collect and store.